CacheStorage: Use task_runner_ in CacheStorageScheduler.

This CL implements changes that were intended to be in
crrev.com/c/1599304.  That CL passed the SequencedTaskRunner down to
the scheduler, but neglected to actually use it when scheduling
operations.

Bug: 960012
Change-Id: Ieb92bb99cd7e864971f993d2eeb5ef65f49b3b2e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1623205
Commit-Queue: Ben Kelly <wanderview@chromium.org>
Commit-Queue: Victor Costan <pwnall@chromium.org>
Reviewed-by: Victor Costan <pwnall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#661911}
1 file changed